Ionic liquids, also referred to as room-temperature-molten salts, have attracted special attention for the past several years, owing to their potential uses as electrolytes for a variety of electrochemical devices such as lithium secondary batteries, solar cells, actuators, electric double-layer capacitors and the like, reaction media, and catalysts for organic syntheses. Compared with conventional organic liquid electrolytes, ionic liquids as electrolytes have the main advantages of flame retardance, non-volatility and high thermal stability. Bistrifluoromethylsulfonylimide ([(CF3SO2)2N]−) and tetrafluoroborate (BF4−) have attracted attention as anions for most of the ionic liquids so far reported, because of their high electrochemical stabilities and thermal stabilities (Patent Documents 1 and 2). However, ionic liquids containing these anions have suffered from problems such as, in particular, low conductivities at low temperatures.
Patent Document 3 discloses boron compounds; however, for example, triethylmethylammonium CF3BF3 manufactured in the Examples has a melting point as high as 181° C., and therefore is not an ionic liquid. Moreover, Patent Publication 4 discloses the BF3CF3 salt of 1-ethyl-3-methylimidazolium in Example 1.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-099001    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-331918    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2002-63934    Patent Document 4: Japanese Unexamined Patent Application Publication No. 2004-123631